1. Field of the Invention
The present invention relates to a read sensor with self-aligned low resistance leads and a method of making wherein the method employs protective capping layers during milling steps for eliminating a masking step in the construction of low resistance lead layer portions of the lead structure.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating. When the disk rotates air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The read head includes a read sensor that is located between first and second gap layers and the first and second gap layers are located between first and second shield layers. The first and second gap layers magnetically insulate the read sensor from the shield layers and the shield layers protect the read sensor from stray magnetic fields. Accordingly, the read sensor is sensitive to flux signals from the rotating disk within the distance between the first and second shield layers. This distance defines the linear density capability of the read head. The smaller this distance the greater the linear density and the more information that can be read by the read head per track length.
The flux signals imposed on the read head change the resistance of the read sensor. By conducting a sense current through the read sensor the processing circuitry can detect a change in potential when the flux signal changes the resistance of the read sensor. In a digital scheme where ones and zeros convey information the flux signal can represent a one and the absence of a flux signal can represent a zero. Accordingly, incremental lengths of the track represent bits of information in the digital scheme. The greater the linear density, the greater the number of bits of information that can be read by the read head from the track on the rotating disk.
The read sensor can be an anisotropic magnetoresistive (AMR) sensor or a spin valve (SV) sensor. Either of these sensors is sensitive to flux incursions so that when the sense current is conducted through the sensor potential changes can be detected by the processing circuitry. The sense current is conducted through the read sensor by first and second leads that are connected at opposite ends of the read sensor. The first and second leads are located between the first and second gap layers which electrically insulate the leads from the shield layers. A portion of each of the leads is exposed at the aforementioned ABS where they are subjected to corrosion. An anticorrosion and mechanically stable material is selected for these lead portions, such as tantalum (Ta). Unfortunately, Ta is also highly resistive. These lead portions are referred to as the high resistance lead portions. At a recessed location in the head a low resistance lead portion is stitched (overlapping connection) to a respective high resistance portion. The stitching approach also reduces the topography of the lead structure at the ABS. The lead topology, normally replicated into the second shield (first pole piece), can degrade the performance of the write head because of write gap curvature. In the past the high resistance portions extend along the ABS after which they make a bend inwardly for connection to the low resistance portions. This bend has been necessary because of the alignment tolerances in the photomasking process. It would be desirable if the lengths of the high resistance portions could be reduced so as to reduce resistance of the lead structure and heat generated thereby.
The aforementioned lead structure is typically made with three photopatterning (masking) steps. Each photopatterning step involves spinning a layer of photoresist on a wafer where multiple heads are being constructed, light imaging the photoresist layer to prepare portions of the photoresist layer that are to be removed and then removing the photoresist portions with a developer. Milling, such as ion milling or etching is then employed to remove layer portions exposed by the open portions of the photoresist layer.
After applying a layer of read sensor material to the wafer a first mask may be employed for making the high resistance lead portions and defining the track width of the read sensor. Read sensor material exposed by the openings are milled away and high resistance material is deposited to form the high resistance lead portions. By this method side edges of a partially completed read sensor and the high resistance leads abut one another making them self-aligned with respect to one another. A second mask covers the high resistance lead portions and a read sensor site. Milling is then employed to remove a remainder of the read sensor material leaving only the read sensor and the high resistance lead portions connected thereto. A third mask then covers the read sensor and portions of the high resistance lead portions leaving each high resistance lead portion with a stitch region. Low resistance material is then deposited which forms low resistance lead portions that are stitched to the high resistance lead portions and which extend to terminals. It would be desirable if one of the masking steps could be eliminated without degrading the lead structure.
The present invention employs only two masking steps in the construction of the lead structure of the read head. The third masking step, which is employed for constructing the low resistance lead portions, is eliminated by the present invention. This is accomplished by employing protective capping layers that are deposited at various stages of the construction so that milling without a photoresist mask can be employed for constructing the low resistance lead portions. The capping layers are different materials and the dry etching is of different types so that preferential etching can be performed. Preferential etching means that during a selected etching step one or more of the capping layers is etched significantly slower than the other layers. The capping layers are preferably selected from the group C, Al2O3 and SiO2 and the etching is based from the group O2, Ar, fluorocarbon and chlorine containing gases. As an example, an O2 based reactive etching will remove the C cap and leave a Ta cap essentially intact, an Ar based milling will remove the Ta cap and unwanted read sensor material, a fluorocarbon based etching will remove the Ta cap without essentially etching the C and Al2O3 caps and the Ar based milling will remove the unwanted copper or gold without significantly etching the C and Al2O3 caps. By appropriately locating these capping layers and selecting appropriately based etching a lead structure with low overall resistance can be produced with less photomasking steps.
The present method lends itself to constructing a lead structure that has a lower resistance than prior art lead structures. Each of the low resistance lead portions has a front edge that is coextensive with a back edge of the read sensor. Each of first and second high resistance lead portions has a side edge that is contiguous with a side edge of the read sensor (self-aligned) and has a recessed portion that overlaps a respective low resistance portion. Accordingly, the lengths of the high resistance portions is minimized. The widths of the high resistance portions at the ABS is greatly reduced. Instead of making a bend each high resistance portion extends straight back into the head and overlaps a respective low resistance lead portion. With this arrangement resistance is reduced and corrosion of the lead structure at the ABS is reduced.
An object of the present invention is to provide an improved method of making a lead structure of a read head.
Another object is to make a read sensor and first and second leads connected to the read sensor with only two masking steps.
A further object is to selectively employ various capping layers and chemically based dry etching for eliminating a masking step in the construction of a lead structure of a read head.
Still another object is to provide a method of making a read head that enables a reduction in the resistance of a lead structure and reduced corrosion of the lead structure at an air bearing surface.
Still a further object is to provide a lead structure that has a reduced resistance.
Other objects and advantages of the present invention will be appreciated upon reading the following description taken together with the accompanying drawings.